Conventionally, in a refrigeration cycle apparatus such as an air-conditioning apparatus, a refrigerant container for storing excess refrigerant is installed to prevent insufficiency in a refrigerant circuit due to a change in operation condition. One such refrigerant container is an accumulator installed at the suction side of a compressor and temporarily stores the refrigerant flowing out from an evaporator. Another such refrigeration container is a receiver disposed at a position through which the refrigerant in an intermediate pressure state flows and temporarily stores the refrigerant flowing out from a condenser or an evaporator.
Among the aforementioned refrigerant containers, the accumulator installed at the suction side of the compressor is required to have a function to store excess refrigerant. In addition, the accumulator is required to have a function to reduce a liquid back amount for preventing excessive liquid back the compressor and to assuredly return refrigerating machine oil flowing out from the compressor together with the refrigerant, to the compressor without storing the refrigerating machine oil in a large amount within the container. The amount of excess refrigerant varies depending on operation conditions such as an outdoor air condition and the operating frequency of the compressor. In general, under a low evaporating temperature condition, the amount of the circulating refrigerant tends to be small, and the amount of excess refrigerant tends to be large. On the other hand, under a high evaporating temperature condition, the amount of the circulating refrigerant tends to be large, and the amount of excess refrigerant tends to be small.
At a specific temperature or higher, the density of the refrigerating machine oil used together with the refrigerant in the air-conditioning apparatus becomes lower than the density of the refrigerant, so that two-layer separation of the liquid refrigerant and the refrigerating machine oil occurs. The temperature at which the two-layer separation occurs is referred to as separation temperature, and the two-layer separation temperature is different depending on a combination of refrigerant and refrigerating machine oil into two layers to be used. For example, whereas the two-layer separation temperature is equal to or lower than −50 degrees C. when ether oil (PVE) is used together with R410A refrigerant, the two-layer separation temperature increases to about −5 degrees C. when PVE is used together with R32 refrigerant.
In an air-conditioning apparatus including a refrigerant circuit having an accumulator, if refrigerating machine oil whose two-layer separation temperature is high is used, for example, if PVE is used together with R32 refrigerant, two-layer separation of the refrigerating machine oil and the liquid refrigerant occurs under a very low temperature condition (e.g., −20 degrees C.) under which the evaporating temperature of the refrigerant becomes low. As a result, the refrigerating machine oil separates in an upper layer above the liquid refrigerant within the accumulator and thus cannot return to a compressor via an oil return hole in a lower portion of the accumulator, so that seizure occurs at a sliding portion of the compressor. Thus, hitherto, a technique to reduce the amount of the liquid refrigerant flowing into the compressor and to be able to efficiently return a required amount of the oil to the compressor has been proposed (see, e.g., Patent Literature 1).
An existing air-conditioning apparatus includes an accumulator that includes: an airtight container; an inlet pipe and an outlet pipe that communicate within the airtight container; a perforated pipe that has one end connected to the outlet pipe at the outside of the airtight container and has a plurality of oil recovery holes formed along an up-down direction; and a first oil return pipe that has one end connected to the outlet pipe at the outer side of the airtight container and another end opened in a bottom portion of the airtight container. The air-conditioning apparatus is provided with a first opening/closing valve at any position in a connection portion between the first oil return pipe and the outlet pipe, is provided with a second opening/closing valve at any position in a connection portion between the outlet pipe and the perforated pipe at the outer side of the airtight container, and includes two-layer separation detection control means that controls the opening/closing valves by detecting a state of refrigerating machine oil and refrigerant stagnating within the airtight container, on the basis of at least one of the pressure or the temperature of the refrigerant.